Control system for inductionheating apparatus



Feb. 13, 1951 H. A. STRIQKLAND, JR

CONTROL SYSTEM FOR INDUCTION-HEATING APPARATUS 4 SheetsSheet 1 OriginalFiled May 1'7, 1945 1N VEN TOR Harold A. Strickland, d1.

ATTORNEY Feb. 13, 1951 H. A. STRICKLAND, JR 2,541,123

. CONTROL SYSTEM FOR INDUCTION-HEATING APPARATUS Original Filed May 17,1945 4 Sheets-Sheet 2 lll llllllllllllllllm mmmm K maxim 1m 2 ;g 1 3INVENTOR Hamid A. Smck/and J1? 4Q4Z..-:?EZZZL Z:L

ATTORNEY Feb. 13, 1951 H. A. STRICKLAND, JR

CONTROL SYSTEM FOR INDUCTION-HEATING APPARATUS Original Filed May 1'7,1945 4 Sheets-Sheet 3 [Hamid Siffcfdmid, 1/

Feb. 13', 1951 H. A. STRICKLAND, JR

CONTROL SYSTEM FOR INDUCTION-HEATING APPARATUS 4 Sheets-Sheet 4 OriginalFiled May 17, 1945 E IG: 7

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A TTGENEY Patented Feb. 13, 1951 CONTROL SYSTEM FOR INDUCTION- HEATINGAPPARATUS Harold A. Strickland, J r., Detroit, Mich., assignor, by mesneassignments, to The Ohio Crankshaft Company, Cleveland, Ohio, acorporation of Ohio Original application May 17, 1945, Serial No.594,329. Divided and this application July 8, 1946, Serial No. 681,996

2 Claims. (01. 219-13) This invention relates to apparatus for heatinginductively workpieces adapted to move progressively through the heatingcoil of the apparatus and is an improvement over the apparatus shown inapplicants Patent No. 2,325,638, filed September 19, 1941. Thisapplication is a divisional of Serial No. 594,329, filed May 17, 1945,now abandoned.

An object of this invention is to provide a highfrequency inductionfurnace of the type shown Figure 2 is a section of the furnace takenalong the line 2-2 of Figure 1;

Figure 3 is a view indicating the transfer point between coil sectionsin the furnace;

Figure 4 is an end view of the workpiece guide element;

Figure 5 is a side view of the workpiece guide; Figure 6 is a view of apart of the workpiece guide; and

Figure 7 is a wiring diagram.

The sectional elevation of Figure 1 illustrates.

the general setup and arrangement of the apparatus for machine generallydesignated by the numeral I. On the base 2 there is mounted a frame 3for enclosure of the capacitor bank I v and for support of the inductionfurnace workpiece feed apparatusand power means. For aid 'in descriptionthe power mechanism will be designated by the letter A, the workpiecefeed apparatus by the letter B. and the induction furnace by the letterC, these units being positioned as shown in Figure 1 from left to rightof the machine. These various units A, B and C are enclosed by a casing5 preferably of non-magnetic material; as aluminum, the casing extendingQn'om enclto end of the machine and nnboth sides and ends as shown inFigures 1 and 2. Preferably the casing is divided transversely intosections 5a and 5b, section Go enclosing the induction furnace andsection 5b the feed mechanism and power unit.

Referring first to the workpiece feeding unit B there is provided achute 6 which extends angularly from the top casing 5 in position toreceive a number of workpieces which for purposes of description will bereferred to as billets. These billets have a length corresponding to thewidth of the chute and are adapted for placement side by side in thechute for feeding into the billet channel 1 at the base of the chute. Asupply chute switch 83 opens the power circuit when the supply ofbillets fails. As fully described in applicants patent above-mentionedthe channel 1 is open at either end and from the power side is adaptedto receive power application from the A unit including the plungerelement 8 pivotally connected to a connecting rod 9 adapted forreciprocation by the pulley and belt mechanism shown. A motor [0 isconnected to the shaft of the lower pulley, the screw shaft l I and handwheel I2 affording means for adjusting the tension of the belt.

On the side of the billet channel 1 adjacent the furnace a channelextension (3 is provided into which billets are moved by the projector 8from the channel I as they are fed downwardly in the chute 6 by gravity.This feeding action is intermittent in accordance with the reciprocationof the plunger 8 and the projected billets are lined by this action ofthe mechanism end to end in the channel I3. As the movement continuesthe billets are moved through the guide grid" to the heating chamber ofthe furnace. The guide grid is of special construction comprising tworight angled sections 15 and it, one of which is shown in Figure 6,which, on being united, form a member with a square contour having asolid base of flat stock from which extend projecting fingers I1. Thesefingers are roughly triangular in shape with the flattened sides of theplates in a given unit each parallel with each other. The inner edge [8of these plates is preferably formed of hardened material as these edgesconstitute the bearing surface of the grid and may be formed of separatestrips attached to the plates 11. The bearin edge or. the pla e I. i bsantia sections :25, 26 and .21.

-' i'tFig. 1'3). the lugs 33 with a cutoff corner on the'end at aparallel with the axis of the furnace and so positioned relative to thisaxis that the center of the exit opening of the grid is coincident withthe heating channel axis. Adjustment of the grid, so as to permitcentering thereof in relation to the coil axis, is possible from theconstruction of the grid in two sections, the attachment bolts i9 beingof lesser diameter than the attachment apertures 20 on the grid topermit relative movement .of the sections with reference to each other.By such movement the center of the grid axis opening may be shiftedlaterally.

The induction furnace C is positioned in extension of the grid 14 asshown in'Figu-ne 1; This unit includes three sections 25, 26 and 21 incommon alignment and formed :as compl'ete Iuriits independent of eachother andseparably remov able. Each unit comprises a heating -coil -28wound in square formation of square sectioned copper tubing, the turns=of the coil being insulated from each other. Interiorly :of the cellare a plurality of insulation blocks 29 (Fig. 2) supported in place bymetal tubes or rails 31) provided with butterfly supporting plates 31.'These plates are attached to the rails 33 on the inner -sides thereofwith lateral extensions adapted to "overlie the-adjacent edges --'of therefractory iire brick or other material used as hea'ting insulationmaterial, thus reta'ining this material :in

place.

The rails 39 function as cooling rneans', :the profleeting ends thereofb'e'ing -ou't'turn'ed and attached to supply sources 32 of a :coolant."The also serve to support lugs '33 :consisting of small platesedge-attached at displaced points along the inner =usrface :of the rails:as shown in oo-pending application :Serial No. 384,503, filed March 21,1 941, new Patent "No. 2,408,350

deited :Septemb'er 2l4, 1946. 1A5 will :be seen from inspection :of.Figure T2 the rlugs 35 are in close proximity to the billets on ail:sijdes thereof so =tha tbuckling "of the train of billets ininovementthrough theifurnace chamber is prevented. The :lugs '33 .shoul'dloe ofheat :resistant metal so as ito withstand high temperatures present inthe 5fiurnace during operation.

:Externalto the "coil =28 :there ;-is :a layer -01" insuilat'mg slabsBQ-Whichmay be of Transite. At the sends :of :the co'iLsupport plates-,%5 are provided to which the heating .coil -unit is attached byfmeansof rods 36, there being four of these .redsshown Figure *2 extendingexternal 'to the coil from :end to endand retained by means ofhookedsup- .iports 3:! on the outer-face of theend plates 35.

Coil connections from each coil for supply icf electrical power is ibymeans of :the coil taps 2i, '0 qconnecting traps 3'8 and bus bars :33,Ali-and 41 "The "capacitors -42 are :connected by straps :43 to and F45mounted on the :coolant tubing -;inter- .mediate "the end plates 35 :of:adjacentsections These lugs :are :in general similar to which thebillet approaches but the "lug 46 is formed with a flatterandmoreextendedtfacexon In :order to insure 'con- At the rear or exitend of the section 21 of the furnace a second guide grill 58 is providedleading into a chute section 5|. A further chute section 52 at the endof the first chute section provides a channel for carrying the heatedbillet to a receptacle external of the machine. A door switch 53comprising a pivoted plate hinged on the side of the chanel so as to beactuated by the :movement of :a passing billet isprovlided. Also in linewith the axis of the furnace ra photo-cell unit 54 containing switchmeans 98 (Fig. 7) is secured to the casing section 5a at the end of thema- .chine, an aperture being made in the casing so thatl'ig'ht from thefurnace may penetrate the unit to modify the resistance of the cell.

ll'tiha's been previously mentioned that the casrings'irhas been dividedinto two sections 5a, and 5b. Theinnenenfisfif these two casings adjoineach other and are supported by an intercepting transverse .plate 55extending across the upper casing :chamber. This plate also supports thegrid [4. iCon-nectionrbetween the plate 55 and the casing ends is bymeans of brackets 55 and 51 which are "bolted respectively to the plateand casing. The

plate is lined, preferably with insulation matesrial :in illhe :form pfinsulation :sheets, upper .edge of which extends 'between the adjoiningredgesaof :casings :5a and '5?) and between :the brackch58 and the plate55580135 zto:insulatecelectrically sboth ca-sings from -:.each other andfrom the brackets 15.6. Insulation also surrounds the bolts .58 securing{the bracket :56 to -the plate 55. ,Ad-

ditional insulation of the casingi'is -proyided inan :insulation get-rip:59 placed :between the .bracket 26%] and :the casing plate 61 rasishownin Figure 2. The attaching screw bolt .is also insulated from thebracket 69. In {this manner the electrical including the casing and theplate .5! is interrupted whereby eddyscurrents, .due .to .fluxtransmitted by the heating coils, are eliminated.

It is pointed out .f-urther-asrshown-in Figure 2 that there is providedflux return paths ior the .-coil in the 52 secured along the inner:suriface of the casing 5a. These .fiux .return units comprise laminatedstrips 63 placed in :slotted "tubes 64 where they are retained .bythe:fiber linking 65 and plate 68. These aextend longitudinally of theleasing parallel to the heating .coil and reducethe eddy currents .inthe casing ;-to such :an extent that heating .efiects therein arepractically eliminated. Without these flux meturn units the-casingbecomes sohot thatit is a source of danger to the attendants.

InFigure 5710f the drawing is indicated a wiring diagram of the circuitwhich is applicable :to the machine as hereinabove described. The :useof :threemhase alternating purreut is indicated as being applied toinlet source terminals 10, 1i and 12. From source .10 :the circuit leadsthrough a gmainzmanualiswitch 1-.3,-nnd2a. relay iSWitGh .74 to themotor :15 .for operating the equipment. ,Enom source J1 the .circuitleads through manual switch 16 to the mainiconductor 1,1 andirom'sourceJ2 through manual switch 1-8 to the main :conductor 39. The circuitinvolves .six sections referred .to :as :sections 113 G, .H :and vI.;S,ection 134mmprises the :motor ;;pilo.t :circuit and includes therpilotrizelay coil :80, the manual motongstantrswitch 8; l, th'ezmanualmotor .stopningnwitch 2 ,:the nor- 7 :mally "open supply phute -switch$3., the :normally closed line switch ".84 and "the normally open :timer.chute "manual zswitch :85. A pilot lamp :86

:is provided "also in parallel with .thcpilot coil 7.80 to indicate.,current :fiow .in ?this branch icircnit.

manual switch II is provided. The E branch circuit includes the motor15, the relay switch 14, the relay switch 81 between the motor and themain conductor 11 and the relay switch 80 between the motor and the mainconductor 19. These switches are normally open and on closure cause themotor to function.

Branch F of the circuit is the timer section. The timer may be of anyknown construction such as the Eagle timer and includes a clutch coil 09a motor 90 and a normally closed relay switch 9i, the motor and switchbeing in series across the main conductors I1 and 19. The clutch coil isin series with the normally open delivery switch 53 between theconductors I1 and I9. The timer circuit also includes the timer switch93 which normally is open but remains closed during the operation of themachine unless the movement of billets is interrupted.

Branch G of the circuit includes the intermediate contactor coil 94 inparallel with the indicating lamp 95, the normally open manual switch96, the normally closed manual switch 91, the normally open door switchIll, the normally closed photo-cell switch 98, the normally open coolantpressure switch 99 and the normally open flow switch I00, each of theseelements being connected in series from the conductor 11 to a pointbetween the pilot coil 80 in the D circuit and the manual motor startingsw tch 8|. A normally open relay switch IOI shunts the manual switch 90in the intermediate contactor circuit.

The main contactor circuit H includes the bridge rectifier I02 connecteddirectly to the conductor l1 and, through the relay switch I03 andresistor I04, to the conductor 19. A normally open relay switch I05by-passes the resistor I04. The rectified c rcuit comprises the normallyopen relay switch I and the main contactor coil I01 which functions toclose the heating circuit. The armature of this coil when closing alsocloses switch I after the first current surge through the H circuit. Theheating circuit I includes the normally open relay switch I00 and theheating coil I09 energized from the high frequency power source IIO.

Additionally, the circuit includes the lamp indicator I I I to indicatepower in mains I1 and I9, and lamp I I2 and normally open pressureswitch I I3 to indicate proper coolant pressure in the furnace tubing.

In operation, with the door switch II4 closed, the coolant circuits forthe support rails and heating coils are supplied with coolant underpressure thereby causing closure of pressure and flow switches 99, I00and H3 in the G branch circuit. Billets are placed in billet chute 0,closing switch 83. The motor switch 8| is then closed manually therebycompleting a circuit through the pilot coil 80 and lamp 88. Energizationof coil 80 closes relay switch II5 locking the coil 00 and permittingstarting switch 8i to be opened. Also relay contacts I4, 81 and 88 areclosed to energize the motor I5 and start the feeding mechanism. Billetsare consequently intermittently moved fro-m the base of the chute intothe furnace for heating by the heating coil. Simulta neously theintermediate contactor manual switch 96 is closed energizing coil 94 andcausing closure of relay switch IOI to lock in the coil circuit, Alsothe contact switches I03 and I06 are closed in the H contactor circuitsupplying direct current to contactor coil I01 to close switch I05 andthe heating circuit I. If there is no obstruction in the movement of thebillets it will be continuous and uniform and as each successive billetleaves the exit grid 50 and moves down the chute 52 it will operate thestock delivery switch 53 causing closure of the same and energization ofthe timer clutch coil 89. Thereupon timer switch 93 closes and the timerbegins a cycle which is substantially in excess of the time necessary tobring a billet to the required temperature in moving through thefurnace. Consequently the billet will pass out of the furnace and downchute 53 before the timer cycle is completed and in so doing operatesthe delivery switch 53 to cause a resetting of the timer, the timerswitch 93 remaining closed. After another time interval and before thetimer completes its new cycle another billet emerges from the exit gridand operates the chute stock delivery switch. This sequence ofoperations will continue indefinitely as long as the supply of billetsin the supply chute is maintained and as long as there is nointerruption in the movement of billets through the furnace. Should thesupply of billets fail or should a stoppage occur in the furnace for anyreason or should the power mechanism for supplying billets to thefurnace be interrupted the timer will then tune out, switch 93 will openand motor 15 will stop through opening of the associated switches '14,81 and 88. On the opening of timer switch 93 timer motor switch 9i alsoopens.

After stoppage due to any of the causes mentioned, a restarting of themachine can be accomplished only by actuating the stock delivery switch53, assuming that the supply, pressure and flow switches are closed.When this occurs timer switches 9i and 93 close and the timer resets foranew cycle.

In the event that through excess voltages or other causes the heat inthe furnace becomes excessive the photo-cell switch 98 opens therebydeenergizing the heating circuit but not interrupting the motor circuitso that the billet movement continues until the temperature has fallenin the furnace to a normal value.

Modifications in structure and circuit may be made within the scope ofthe claims hereto appended.

What is claimed is:

1. In a machine for progressive heating of a train of workpieces; aninduction heating chamber therefor, means for supplying a train ofindividual workpieces, power means for moving said train through saidchamber, a high-frequency power source for heating workpieces in saidchamber, means for interrupting the power means and power source onfailure of said train of workpieces to move upon actuation by said powermeans, and additional means for interrupting the power source alone ondevelopment of abnormal heat in said chamber, said last-mentioned meanscomprising controls actuated in response to the temperature of emergingworkpieces.

2, In a machine for progressive heating of a train of workpieces; aninduction heating chamber therefor, means for supplying a train ofindividual workpieces, power means for moving said train through saidchamber, a high-frequency power source for heating workpieces in saidchamber, means for interrupting the power means and power source onfailure of said train of workpieces to move upon actuation by said powermeans, and additional means for interrupting the power source alone ondevelopment of abnormal heat in said chamber and for connecting thepower supply on reduction of heat to normal in said chamber, saidlast-mentioned means oom-

